What if Bismarck hit Rodney early on?

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dunmunro
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Re: What if Bismarck hit Rodney early on?

Post by dunmunro » Mon Sep 10, 2018 8:06 pm

alecsandros wrote:
Mon Sep 10, 2018 7:36 pm
dunmunro wrote:
Mon Sep 10, 2018 7:32 pm

The blue line shows a travel of 76ft... The shell has to penetrate the hull plate for a ~10% velocity loss and then a 12in bulkhead for another huge loss of velocity. The pink line is 93ft long and the bulkhead it passes through is 8in thick. (R&R British Battleships page 123)
Where did you get 10% velocity loss when passing through 37mm of contruction steel ?

As known, 12" (305mm) and 8" (203mm) respectively is easily perforatable by 380mm shot from 18000meters. Shot has velocity of ~525m/s, enough to perforate ~440mm (17") of solid plate of better quality then the 1920s armor.
see http://www.kbismarck.com/38cm.html
Okun's programs are good enough for a ballpark figure, and you have to remember the extreme inclinations involved. There's a huge difference between passing through a 1.5in plate at normal (0deg) and at ~76 degs.

You don't assume any velocity loss at all, even when passing through 12in plate.

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Re: What if Bismarck hit Rodney early on?

Post by dunmunro » Mon Sep 10, 2018 8:20 pm

alecsandros wrote:
Mon Sep 10, 2018 7:44 pm
The RN did a post war study of Nelson class armour and concluded that it was essentially identical to WW2 armour. See ADM 281-40.
in some tests yes,
in others, it was worse then KGV type of cemented armor by up to 10%.
Friedman, in "The British Battleship 1906-1946", writes (pg 371): "when HMS Rodney was scrapped, N.C.D. compared her (1923) armor with later types. The testers concluded that modern armour, such as that on HMS Vanguard, was only slightly better than the armor in Rodney, but it was more consistently effective "
From the original study:

6) Conclusions

There is no significant difference in the penetrative resistance of
C. armour, when comparing present day armour with that of the armour used
in H.M.S, RODNEY in 1923, The modern armour is however more consistent,
there being much less scatter in the results.

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Re: What if Bismarck hit Rodney early on?

Post by alecsandros » Tue Sep 11, 2018 5:24 am

dunmunro wrote:
Mon Sep 10, 2018 8:06 pm
Okun's programs are good enough for a ballpark figure, and you have to remember the extreme inclinations involved. There's a huge difference between passing through a 1.5in plate at normal (0deg) and at ~76 degs.
You don't assume any velocity loss at all, even when passing through 12in plate.
At such high obliquities, I doubt the 12" bulkhead could be perforated.

But why do you consider the obliquities so high ?

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Re: What if Bismarck hit Rodney early on?

Post by dunmunro » Tue Sep 11, 2018 9:28 am

alecsandros wrote:
Tue Sep 11, 2018 5:24 am
dunmunro wrote:
Mon Sep 10, 2018 8:06 pm
Okun's programs are good enough for a ballpark figure, and you have to remember the extreme inclinations involved. There's a huge difference between passing through a 1.5in plate at normal (0deg) and at ~76 degs.
You don't assume any velocity loss at all, even when passing through 12in plate.
At such high obliquities, I doubt the 12" bulkhead could be perforated.

But why do you consider the obliquities so high ?
The original premise was this:
Bismarck supposedly only fired 3 salvos from her fore turrets before they were silenced, these are recorded as: short, straddle, over.

So Campbell's account said that Bismarck's 3rd salvo from the fore turrets, just before Rodney obtained 1-2 hit(s) on them to take them out of action achieved a 'perfect straddle' with shells landing, fore, aft and to both sides. In short, he seems to have described the shells as almost hitting but just barely missing. In fact the shells did cause some damage, fragments knocked the AA director station out of action but killed no one (I'm actually curious as to this as most accounts mention no damage at all to Rodney or KGV during the final engagement, did this actually happen or was minor damage simply discounted as it wasn't a direct hit?).

Now the what if:

What if those shells had instead hit? Could it have achieved a mutual kill with Bismarck's fore guns going out of action but with Rodney's firepower being effectively silenced as well? As the approach was bow on, Rodney's armor would have counted for nothing, there is no effective armor in the bow on angle of a ship, had Bimarck's shells hit, depending on where they hit, they could very well have done another "Hood" as Campbell's account recorded.
We have Rodney steering almost directly towards Bismarck so by definition the 38cm shells would have to strike the deck or hull with very high inclination (~75 degrees from the normal) that would be nearly equal to the AoF of the shell. Again, by definition the shells, with their flat trajectory have to then find their way into a magazine, and as we've seen this is going to be very difficult as the shells will strike the deck/hull plating and then tear through a lot of ship's structure prior to striking the armoured bulkhead. Consequently the odds of a functioning shell making it all the way to a magazine is nil. In fact the odds of a functioning shell even making it to the armoured bulkhead before detonating are very low.

Okun's penetration programs indicate that the shell would likely richochet from the hull/deck when striking at such an oblique angle and the 38cm GKDOS table ends at 70 degs from the normal.

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Re: What if Bismarck hit Rodney early on?

Post by alecsandros » Tue Sep 11, 2018 11:25 am

dunmunro wrote:
Tue Sep 11, 2018 9:28 am
Again, by definition the shells, with their flat trajectory have to then find their way into a magazine, and as we've seen this is going to be very difficult as the shells will strike the deck/hull plating and then tear through a lot of ship's structure prior to striking the armoured bulkhead. Consequently the odds of a functioning shell making it all the way to a magazine is nil. In fact the odds of a functioning shell even making it to the armoured bulkhead before detonating are very low.
75deg obliquity when striking the hull, yes, it's probable.

About 30deg obliquity when striking the forward armored bulkhead (15deg A0F + 15deg lateral obliquity, as Rodney wasn't exactly head on).

At 18000meters , 380mm APC shell falls at angle of 13,9deg with velocity of 532m/s. First impact, or impacts , with hull elements will strip the windscreen off (83kg mass) and initiate the fuze. The remaining mass of 717kg will push through the structure until hitting the bulkhead (305 or 203mm thickness depending on the trajectory).

Fuze is considered in 'Loss of HMS Hood ' (http://www.zhanliejian.com/navweaps/INRO_Hood_p3.htm#62) as follows:
62 Evidence from U.S. sources indicates that such an increase in delay would not be unusual. For example, U.S. Navy specifications for the Base Detonating Fuze Mark 21 considered the fuze action satisfactory if the detonation occurred between 0.030 and 0.070 seconds after impact when set for a nominal 0.033 second delay. British experience at the River Plate and elsewhere lead them to estimate the effective German fuze delay as being about 0.05 seconds.


0,03sec with 532m/s = 15,96meters (52,67feet) (in reality less then that as every obstacle would slightly decrease velocity, and perforation of armored bulkhead would reduce it very much)
0,05sec with 532m/s = 26,60meters (87,78feet) (" …………………….")
0,07sec with 532m/s = 37,24meters (122,90feet) (" …………………….")

---

Therefore it all rests on the actual way in which the fuze would work (and IF it would work - although having a dud projectile crashing at 400m/s into the forward main magazine can also produce catastrophic damage. At Denmark Strait, a dud 380mm shell hit Prince of Wales ~8meters below the waterline, suggesting that the underwater trajectory was about 40 meters (132feet), based on range 16km, angle of fall ~12degrees, depth of hit 8meters. Sin(12degrees) is 0,20).

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Re: What if Bismarck hit Rodney early on?

Post by dunmunro » Tue Sep 11, 2018 9:04 pm

The hull sides on British cruisers were only .5- .75in thick. This was not enough to reliably trigger a base fuze, despite that the longest travel for a shell that detonated was 64 ft on Exeter (at 0644 and ~11500yds range- Battle Summary 26)* which was only ~.032 seconds, assuming an SV of 2000fps. This shell didn't strike the hull side but passed through much light plating:
Hit No.6 passed through the wheelhouse charthouse, out through the armament office and
exploded just forward of the starboard 4 inch HA Gun. Damage from splinters was
widespread, ammunition in RUs lockers was ignited, the lower bridge and 25% of the
4 inch armament was put out of action. ( Ships Damaged or Sunk by Enemy Action)
Anyways, unless we invoke supernatural forces to permit 38cm shells to retain their AP cap at extremely high impact inclinations, where the sheering forces are extreme, then give an extraordinary delay to KM AP fuzes, then allow for zero yaw effect despite the high inclination and the collisions with further ship's structure, so that the capped AP shell can strike the armoured bulkhead at an optimum angle and pass through while suffering almost no reduction of velocity, there's no way for a 38cm shell to reach a magazine with Rodney steering directly at Bismarck.

I think I'll pass on further comments on this aspect of the topic.


*During this phase of the action Exeter had closed the considerably and had just turned to fire her port torpedo tubes at a range to target of 11000 yds.

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Re: What if Bismarck hit Rodney early on?

Post by alecsandros » Wed Sep 12, 2018 4:00 am

380mm armor piercing shots are not decapped or yawed by construcion grade steel of 37mm thickness. The only armor grade material in way of the shot is the armored bulkhead itself.

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Re: What if Bismarck hit Rodney early on?

Post by alecsandros » Wed Sep 12, 2018 4:13 am

British investigation into the loss of HMS hood (boards of enquiry) worked with experts that mentioned the fuze delay considered for Graf Spee's APC shots at River Plate were 0,05sec.

The article I posted above mentions 0,03 to 0,07sec - with 0,07s being the working time for one of the possible trajectories that destroyed HMS Hood.

German Bz38 base fuze was normally expected to explode some 0,03 to 0,04seconds after being initiated, with the initiation itself lasting about 0,003sec (therefore total time is 0,033 to 0,043sec IF working as designed). Thorsten has good info on the subject.

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Re: What if Bismarck hit Rodney early on?

Post by alecsandros » Wed Sep 12, 2018 5:52 pm

As a closing thought on the subject,
HMS HOOD's 15" guns scored a remarkable hit against French Dunkerque at Mers-el-Kebyr in 1940: the 4th hit obtained on the French battlecruiser struck the main belt (225mm thick incline at 15deg), from 17500yards (probable impact velocity 480m/s or 1584 feet/s), perforated the main belt, and travelled ~13meters (based on Jordan and Dumas drawings) before exploding inside the boiler room. Calculating exit velocity with facehard gives approx 820feet/s or 248,6m/s. As the trajectory was 13 meters (43feet) , with the data above, the length of time between impact of shell against the plate and explosion was approx 0,052seconds, almost exactly 200% more then the typical fuze-delay length of British shell (which was 0,025sec).

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Re: What if Bismarck hit Rodney early on?

Post by dunmunro » Wed Sep 12, 2018 9:53 pm

alecsandros wrote:
Wed Sep 12, 2018 5:52 pm
As a closing thought on the subject,
HMS HOOD's 15" guns scored a remarkable hit against French Dunkerque at Mers-el-Kebyr in 1940: the 4th hit obtained on the French battlecruiser struck the main belt (225mm thick incline at 15deg), from 17500yards (probable impact velocity 480m/s or 1584 feet/s), perforated the main belt, and travelled ~13meters (based on Jordan and Dumas drawings) before exploding inside the boiler room. Calculating exit velocity with facehard gives approx 820feet/s or 248,6m/s. As the trajectory was 13 meters (43feet) , with the data above, the length of time between impact of shell against the plate and explosion was approx 0,052seconds, almost exactly 200% more then the typical fuze-delay length of British shell (which was 0,025sec).
The main belt is inclined 11.5 degrees. The outer hull plate is only 10mm which is not enough to reliably activate the fuze. My calculations show about 1100fps velocity remaining after penetration.

Jordan and Dumas' drawings show a total travel of ~10.5 meters from the armour belt to point of detonation (hint - hull depth, armoured deck to keel, is about 13.6 meters). This gives about a .032 delay.

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Re: What if Bismarck hit Rodney early on?

Post by alecsandros » Thu Sep 13, 2018 4:07 am

The drawing is an exact semi-section of the ship at boiler 21. Beam was 30meters, thus semi section 15meters. You need to calculate the trajectory length, not it's horizontal projection to rhe deck.

For impact I worked with 480m/s capped 6crh shell of 1940 vintage versus 9inch plate at 20 deg (total obliquity at the point of impact, coming from shell angle of fall and plate declination )

248,6m/s with projectile in complete working order is what I obtained

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Re: What if Bismarck hit Rodney early on?

Post by dunmunro » Thu Sep 13, 2018 5:16 am

alecsandros wrote:
Thu Sep 13, 2018 4:07 am
The drawing is an exact semi-section of the ship at boiler 21. Beam was 30meters, thus semi section 15meters. You need to calculate the trajectory length, not it's horizontal projection to rhe deck.

For impact I worked with 480m/s capped 6crh shell of 1940 vintage versus 9inch plate at 20 deg (total obliquity at the point of impact, coming from shell angle of fall and plate declination )

248,6m/s with projectile in complete working order is what I obtained
If the semi-section is 15 meters then the arrows representing the shell path are 9.3 and 10 meters (upper and lower) respectively from armour belt to point of burst. It is obvious that the arrows are about 2/3 the semi-section width. Remember that length begins at the armour belt, not the hull plating because it is too thin for fuze activation.

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Re: What if Bismarck hit Rodney early on?

Post by alecsandros » Thu Sep 13, 2018 8:06 am

dunmunro wrote:
Thu Sep 13, 2018 5:16 am
If the semi-section is 15 meters then the arrows representing the shell path are 9.3 and 10 meters (upper and lower) respectively from armour belt to point of burst. It is obvious that the arrows are about 2/3 the semi-section width. Remember that length begins at the armour belt, not the hull plating because it is too thin for fuze activation.
I think you are looking at diagram of hit no3... The one in question is hit no4.

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Re: What if Bismarck hit Rodney early on?

Post by dunmunro » Thu Sep 13, 2018 8:43 am

alecsandros wrote:
Thu Sep 13, 2018 8:06 am
dunmunro wrote:
Thu Sep 13, 2018 5:16 am
If the semi-section is 15 meters then the arrows representing the shell path are 9.3 and 10 meters (upper and lower) respectively from armour belt to point of burst. It is obvious that the arrows are about 2/3 the semi-section width. Remember that length begins at the armour belt, not the hull plating because it is too thin for fuze activation.
I think you are looking at diagram of hit no3... The one in question is hit no4.
Yes hit 4 (section K). The diagram for hit 4 is below the diagram for hit 3.

I measure 624 pixels for the hull side to the edge of the semi-section and 416 pixels for the length of the arrow so if 624px = 15m then 416px = 10m.

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Re: What if Bismarck hit Rodney early on?

Post by alecsandros » Thu Sep 13, 2018 10:38 am

dunmunro wrote:
Thu Sep 13, 2018 8:43 am
alecsandros wrote:
Thu Sep 13, 2018 8:06 am
dunmunro wrote:
Thu Sep 13, 2018 5:16 am
If the semi-section is 15 meters then the arrows representing the shell path are 9.3 and 10 meters (upper and lower) respectively from armour belt to point of burst. It is obvious that the arrows are about 2/3 the semi-section width. Remember that length begins at the armour belt, not the hull plating because it is too thin for fuze activation.
I think you are looking at diagram of hit no3... The one in question is hit no4.
Yes hit 4 (section K). The diagram for hit 4 is below the diagram for hit 3.

I measure 624 pixels for the hull side to the edge of the semi-section and 416 pixels for the length of the arrow so if 624px = 15m then 416px = 10m.
Measuring it again today,
I have 233px for the 15m midsection and 170px for the trajectory length (measured from the outer skin until the tip of the arrow)

That means 10,94meters.

I don't know if there was any latteral obliquity involved ? (that would increase the length of the trajectory).

We should also take into account the retardation caused by the slope armor and armored torp bulkhead.
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